Oliver Letterer OliverLetterer

Response to a question on Twitter:

Either and Promises/Futures are useful and I’ll use them next time they’re appropriate. But outside Haskell does their monad-ness matter?

(All code below is written in some made-up Java-like syntax, and inevitably contains bugs/typos. I'm also saying "point/flatMap" instead of "return/bind" because that's my audience. Any correspondance with anything that either be programatically or mathematically useful is coincidental)

What is a monad? A refresher.

A monad is something that implements "point" and "flatMap" correctly.

	# Uncomment the next line to define a global platform for your project
	# platform :ios, '9.0'

	target '%TargetName%' do
	# Comment the next line if you're not using Swift and don't want to use dynamic frameworks
	use_frameworks!

	# Pods for %TargetName%
	# pod 'FBSDKCoreKit'
	end

	struct MinimalDecoder : Decoder {
	var codingPath = [CodingKey?]()
	var userInfo = [CodingUserInfoKey : Any]()

	public func container<Key>(keyedBy type: Key.Type) throws -> KeyedDecodingContainer<Key> {
	return KeyedDecodingContainer(MinimalKeyedDecodingContainer<Key>(decoder: self))
	}

	public func unkeyedContainer() throws -> UnkeyedDecodingContainer {
	return DecodingContainer(decoder: self)

	// For https://twitter.com/nicklockwood/status/819938181483233285

	protocol Withable {
	init()
	}

	extension Withable {
	func with(_ body: (inout Self) -> ()) -> Self {
	var copy = self
	body(&copy)

	# The trick is to link the DeviceSupport folder from the beta to the stable version.
	# sudo needed if you run the Mac App Store version. Always download the dmg instead... you'll thank me later :)

	# Support iOS 15 devices (Xcode 13.0) with Xcode 12.5:
	sudo ln -s /Applications/Xcode-beta.app/Contents/Developer/Platforms/iPhoneOS.platform/DeviceSupport/15.0 /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/DeviceSupport

	# Then restart Xcode and reconnect your devices. You will need to do that for every beta of future iOS versions

	# (A similar approach works for older versions too, just change the version number after DeviceSupport)

	$ lldb -- ../build/Ninja-DebugAssert/swift-macosx-x86_64/bin/swiftc -dump-parse ~/GitHub/tmp/hello.swift
	(lldb) target create "../build/Ninja-DebugAssert/swift-macosx-x86_64/bin/swiftc"
	Current executable set to '../build/Ninja-DebugAssert/swift-macosx-x86_64/bin/swiftc' (x86_64).
	(lldb) settings set -- target.run-args "-dump-parse" "/Users/bgesiak/GitHub/tmp/hello.swift"
	(lldb) process launch --stop-at-entry
	Process 91478 stopped
	* thread #1: tid = 0x1bd329, 0x00007fff5fc01000 dyld`_dyld_start, stop reason = signal SIGSTOP
	frame #0: 0x00007fff5fc01000 dyld`_dyld_start
	dyld`_dyld_start:
	-> 0x7fff5fc01000 <+0>: popq %rdi

	void callEntryPointOfImage(char path, int argc, char *argv)
	{
	void *handle;
	int (binary_main)(int binary_argc, char *binary_argv);
	char *error;
	int err = 0;

	printf("Loading %s…\n", path);

	handle = dlopen (path, RTLD_LAZY);

	//Given this:
	NSArray *objects = @[@1, @2, @3]

	//These are equivalent in behavior
	NSNumber *first = [objects objectAtIndex:0]
	NSNumber second = (NSNumber )CFArrayGetValueAtIndex(objects, 0)

	//But is the code that runs the same? Not so much… in the first one we do…
	objc_msgSend(objects, <selector reference>, 0)
	-> http://sealiesoftware.com/msg/x86-mavericks.html

	#!/bin/bash

	# This script downloads and builds the iOS, tvOS and Mac openSSL libraries with Bitcode enabled

	# Credits:
	# https://github.com/st3fan/ios-openssl
	# https://github.com/x2on/OpenSSL-for-iPhone/blob/master/build-libssl.sh
	# https://gist.github.com/foozmeat/5154962
	# Peter Steinberger, PSPDFKit GmbH, @steipete.
	# Felix Schwarz, IOSPIRIT GmbH, @felix_schwarz.

	static NSData PSPDFCalculateSHA256FromFileURL(NSURL fileURL, CC_LONG dataLength, NSError **error) {
	NSCParameterAssert(fileURL);

	dispatch_queue_t shaQueue = dispatch_queue_create("com.pspdfkit.sha256-queue", DISPATCH_QUEUE_SERIAL);
	__block dispatch_io_t readChannel;

	void (^processIntError)(int intError) = ^(int intError) {
	if (intError != 0) {
	PSPDFLogWarning(@"Stream error: %d", intError);
	if (error) *error = [NSError errorWithDomain:@"SHA256Error" code:100 userInfo:@{NSLocalizedDescriptionKey: @"failed to open file for calculating SHA256."}];